1. Field of the Invention
The present invention relates to comparator circuits. More particularly, it relates to a detection circuit capable of receiving a differential input signal and applying a hysteresis proportional to the peak value of the input signal (DCPH). The circuit operates on input voltages that range from a few hundred milli-volts to a few hundred volts.
2. The Prior Art
U.S. Pat. No. 5,019,722 to Hess et al., discloses a threshold crossing detection with improved noise rejection. The output signal from a sensor is integrated and compared with two opposite extreme reference levels corresponding to the amplitude of the integrated sensor signal. Binary signals are latched to one of the two reference levels (high or low) when the respective level is exceeded, and then the signal is further processed to provide an output signal without multiple transitions of noise.
U.S. Pat. No. 4,117,757 to Akamatu, discloses a rectangular waveform signal reproducing circuit for electronic musical instruments which reproduces a rectangular waveform from a monophonic signal having the same fundamental period thereof.
U.S. Pat. No. 3,767,938 to Kueper, discloses a zero sense after peak detection circuit. The circuit provided is a discriminator circuit capable of storing a rejection level which is a predetermined percentage of a valid input signal. Upon exceeding the stored rejection level by a succeeding input signal, an indicator is reset by the input signal whereby a zero crossing detection circuit sets the indicators as the input signal passes through zero volts. A noise signal never exceeds the predetermined rejection level and thus the indicator is not reset.
U.S. Pat. No. 5,015,878 to Lasagna et al., discloses a circuit for processing the signal generated by a variable-reluctance electromagnetic rotation sensor. The circuit described shows the use of a first threshold comparator with hysteresis to provide a reference signal indicative of the zero-crossing of the sensor signal.
In the automotive field, variable reluctance sensors (VRS) are used for detecting the position of the pistons and for measuring the rotation speed of the driveshaft. The VRS consists of an inductive sensor and a toothed wheel that is rotated by the engine. Thus, the signal amplitude from the VRS depends on the rotation speed of the toothed wheel, and can vary from a few hundred millivolts to several hundred volts. Due to the harsh automotive environment, considerable interference is added to this signal. As a result, a comparator circuit with a fixed hysteresis level is not capable of accurately detecting the VRS signal.
The solutions to this problem presented by Hess et al. and Lasagna et al., are problematic in that the phase delay associated with these methods distorts the critical timing information needed to accurately determine the position of the wheel.